added support for auto-detecting the format

This PR adds support for auto-detecting the format typed in rather then having to specify which one to use. Omitting the format option allows the user to type in whatever format they want to use or default in any of the formats rather then picking one up front. Using the first example on the demo page, you can now type in anything (#ffffff, rgb(255, 255, 0), etc..) into the form field and it will set the format accordingly.

It may need some refinement but figured I'd share in case anyone else found this useful.